The present invention relates generally to transfer cases for used in four-wheel drive motor vehicles and, more particularly, to a multi-speed transfer case.
Due to growing consumer demand for four-wheel drive vehicles, a plethora of different power transfer systems are currently utilized for directing power (i.e., drive torque) to all four wheels of the vehicle. For example, in many xe2x80x9cpart-timexe2x80x9d power transfer systems, a transfer case is installed between the front and rear drivelines and is normally operable in a two-wheel drive mode for delivering drive torque to the driven wheels. However, when the four-wheel drive mode is desired, a mode shift mechanism is selectively actuated by the vehicle operator for directly coupling the non-driven wheels to the driven wheels for establishing a part-time or locked four-wheel drive mode.
A significant number of the transfer cases discussed above are equipped with a gear reduction unit and a range shift mechanism operable for permitting the vehicle operator to choose between a high-range and a low-range drive mode. The particular low-range reduction ratio established is dictated by the gear geometry of the gear components associated with the reduction unit and, as such, all conventional two-speed transfer cases have a fixed ratio which ranges between about 2.5 to 4.5 to 1.0. True off-road enthusiasts desire the higher ratio which provides greater tractive ability over the most severe terrain. In contrast, the lower ratio is considered to provide the best tractive results for most typical road and severe weather conditions. Thus, the need exists to provide a multi-speed transfer case that can provide both a high and low reduction ratio mode in addition to the direct ratio mode.
It is an object of the present invention to provide a transfer case for use in four-wheel drive vehicles that is capable of establishing at least three distinct speed ratio drive connections between the input shaft and the output shafts.
As a related object, the transfer case is operable to establish a high-range direct drive connection, a low-range reduction ratio drive connection, and an ultra low-range reduction ratio drive connection.
As a further related object, the transfer case of the present invention is also operable to establish a mid-range drive connection.
As a further object, the three-speed transfer case of the present invention is operable to establish full-time and part-time four-wheel drive modes.
In accordance with a preferred embodiment of the present invention, the three-speed transfer case includes and input shaft, first and second output shafts, and a first planetary gearset having a first sun gear driven by the input shaft, a first ring gear fixed to a stationary member, and a set of first pinions meshed with the first sun gear and the first ring gear and which are rotatably supported from a first carrier. The transfer case further includes a second planetary gearset including a second sun gear, a third sun gear, a second ring gear, a second carrier driving the first output shaft, a set of second pinions rotatably supported by the second carrier and meshed with the second ring gear and the second sun gear, and a set of third pinions rotatably supported by the second carrier and meshed with the third sun gear and the second pinions. A transfer mechanism is provided for driving the second output shaft. The transfer case also includes a range clutch operable in a first state to couple the second ring gear to the input shaft and in a second state to couple the second ring gear to the first carrier; a lock-out clutch operable in a first state to permit rotation of the second sun gear and in a second state to couple the second sun gear to the stationary member; and a mode clutch operable in a first state to couple the transfer mechanism to the third sun gear, in a second state to couple the transfer mechanism to the third sun gear and the second carrier, and in a third state to couple the transfer mechanism to the second carrier.
These and other objects, features and advantages of the present invention will be clearly illustrated and understood upon study of the following written description when taken in conjunction with the following drawings.